[Eternal]

Have you joined any clubs at your school? Those are a great way to meet some people with similar interests. Making friends in college has been tough for me as well because unlike in high school, you won't see these people five times a week. Because of this, you have to be a little more forwards and don't be afraid to ask some people if they'd like to hang out some time. Do you have any co-workers that you think you'd like to hang out with some time? How about people you sit next to during class? It starts with just starting up a conversation. Also if you are living in a dorm go to the events that your RA puts on, even if they sound lame. That will give you a chance to meet people who live on your floor which is a great opportunity to make some friendships.
Remember that three friends isn't bad at all. I'm not sure why it's bad that they are platonic, though? That's what friendships should be. If this one girl stops being a friend to you just because she has a boyfriend, then you don't want her as a friend anyway because friends should always come first before relationships.